Commercial brewing - Managing and maintaining yeast

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Moerdertaktiken

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Hello all!
I was catching up on some reading the other day and came across this paragraph in a book called "Brewery Operations Manual" by Tom Hennessy:

"In theory, and in practice for some breweries, yeast only needs to be purchased once. If it is managed well, it can be regenerated forever. However, most breweries will buy yeast and use it for a specific amount of time, then purchase new yeast."

Now I've been homebrewing for years now, and I've always read that a batch of yeast can only be regenerated 6-7 times before the yeast is no longer viable. Is this correct? How do breweries manage their yeast, and more importantly, how do they maintain their "House" strain? I must be missing something here, and sorry if this is a stupid thread with an easy one-liner answer. I've re-utilized a certain strain in multiple batches before, but have never gone beyond 5 generations.
 
Yeast should only be washed 6-7 times. It can be slanted/plated indefinitely as long as the previous generation remains viable. How else do you think laboratories keep producing a strain of yeast?
 
Usually yeast is pumped cone to cone, meaning after one batch is racked the yeast slurry is pumped from the tank that was racked to the tank preparing to receive wort out of the brewhouse. Commercial production is managed so racking (usually) coincides with brewing another batch on the same day or day either direction.
I have seen small micro breweries use ale pails or specially designed yeast flasks from Sabco in a walk in cooler. Bigger breweries like New Belgium have an entire division devoted to lab services and yeast propagation. They have a seperate yeast storage cellar and an automated system to maintain temperature and possibly feed the yeast.
 
Yeast should only be washed 6-7 times. It can be slanted/plated indefinitely as long as the previous generation remains viable. How else do you think laboratories keep producing a strain of yeast?

Now im as curious as the OP. Is there some type of genetic drift that takes place, on the homebrew scale? If you continue to use and properly store your yeast, could you not use it indefinitely as long as starters are made and viability is verified?

Again, ive always just heard not to use it more than 5 or so batches. What is the scientific reason that you should not go beyond that?
 
ronjonacron said:
Now im as curious as the OP. Is there some type of genetic drift that takes place, on the homebrew scale? If you continue to use and properly store your yeast, could you not use it indefinitely as long as starters are made and viability is verified?

Again, ive always just heard not to use it more than 5 or so batches. What is the scientific reason that you should not go beyond that?

It is more of a hypothesis, even maybe a theory since there is evidence that nature behaves this way in general, but I'm not certain it has been confirmed one way or the other. The idea is that by washing yeast, you are selecting for certain characteristics that may be undesirable, such as high flocculation, or perhaps slow metabolism. After using the same washing process multiple times, you are certainly going to select for yeast that exhibit the characteristics which make it more apt to being harvested with your process. This likely means they exhibit the same characteristics in other areas as well.

Also...and perhaps more worrying...washing is not a sterile process. Bacteria reproduce at a much quicker rate than do yeast, and the more washings you undertake, the higher your risk for infection. It's not that you can't wash yeast forever, it's just that you're potentially risking your beer more and more when you do.
 
Yeast should only be washed 6-7 times. It can be slanted/plated indefinitely as long as the previous generation remains viable. How else do you think laboratories keep producing a strain of yeast?
I guess I should have worded it a bit differently. I was curious of how breweries specifically maintain their "House" strain, or any individual strain for that matter. There isn't a whole lot of literature on yeast management on the commercial scale, which is why this question popped up. I understand that you can slant the first generation and keep it going, but how would one do this on such a massive scale? Do they keep going with 5-6 generations and then ditch it and grow a new population from the slants?
 
It is more of a hypothesis, even maybe a theory since there is evidence that nature behaves this way in general, but I'm not certain it has been confirmed one way or the other. The idea is that by washing yeast, you are selecting for certain characteristics that may be undesirable, such as high flocculation, or perhaps slow metabolism. After using the same washing process multiple times, you are certainly going to select for yeast that exhibit the characteristics which make it more apt to being harvested with your process. This likely means they exhibit the same characteristics in other areas as well.

Also...and perhaps more worrying...washing is not a sterile process. Bacteria reproduce at a much quicker rate than do yeast, and the more washings you undertake, the higher your risk for infection. It's not that you can't wash yeast forever, it's just that you're potentially risking your beer more and more when you do.

I love this post, thanks for your input.
 
Most places will run with the yeast until they see weird behavior. That could be under attenuation, over attenuation, and off flavors. So when that happens, or at a pre-planned interval a fresh prop will be cooked up in the lab. Then used and pitched for.subsequent batches. Its not w big secret. They just use it till its not "right", and buy more or grow their own from their stock.
 
I guess I should have worded it a bit differently. I was curious of how breweries specifically maintain their "House" strain, or any individual strain for that matter. There isn't a whole lot of literature on yeast management on the commercial scale, which is why this question popped up. I understand that you can slant the first generation and keep it going, but how would one do this on such a massive scale? Do they keep going with 5-6 generations and then ditch it and grow a new population from the slants?

Wyeast and White Labs offers proprietary strain services to select, store, maintain and propagate to pitchable quantites.

Or you can do it yourself but somethings are better left to professional labs when you are trying to manage everything else, especially to start. Especially if you don't have time and ingredients to waste on yeast experiments.

Does that help or am I still missing the target?
 
I re use my yeast 10 generations, but have gone longer. If you do simple cell counts with a methalyn blue stain for viability test (there's a crappy video on this on our web site coloradoboy.com) you can keep using it until your viability goes below 90%. If you really want to geek out, grow the original yeast, take a loop and grow some separate colonies on a plate and re-grow those until you die of old age. I like to keep things simple so use your yeast for 10 generation then buy new. You should brew at least once every two weeks or feed your yeast. Cheers!
Tom
 
I re use my yeast 10 generations, but have gone longer. If you do simple cell counts with a methalyn blue stain for viability test (there's a crappy video on this on our web site coloradoboy.com) you can keep using it until your viability goes below 90%. If you really want to geek out, grow the original yeast, take a loop and grow some separate colonies on a plate and re-grow those until you die of old age. I like to keep things simple so use your yeast for 10 generation then buy new. You should brew at least once every two weeks or feed your yeast. Cheers!
Tom
Thanks for the response! Yeah was not expecting a response from THE author! Anyways, thanks everyone for all the comments.
 
Wyeast and White Labs offers proprietary strain services to select, store, maintain and propagate to pitchable quantites.

Or you can do it yourself but somethings are better left to professional labs when you are trying to manage everything else, especially to start. Especially if you don't have time and ingredients to waste on yeast experiments.

Does that help or am I still missing the target?
Yeah thanks! I just started "Yeast: the practical guide to beer fermentation" by Chris White (White Labs) and Jamil Zainasheff. This book is fantastic so far.
 
Now I've been homebrewing for years now, and I've always read that a batch of yeast can only be regenerated 6-7 times before the yeast is no longer viable. Is this correct? How do breweries manage their yeast, and more importantly, how do they maintain their "House" strain? I must be missing something here, and sorry if this is a stupid thread with an easy one-liner answer. I've re-utilized a certain strain in multiple batches before, but have never gone beyond 5 generations.
The answer is "its complicated", so hold on.

Two things happen when you propagate yeast batch-to-batch (either in a commercial, or home environment). The first is the yeasts slowly loose some key biological elements - namely, sterols and unstaruated fatty acids. Both of these require oxygen to be formed, and even with a properly oxygenated wort, eventually run out (the amount of O2 needed to completely regenerate them would lead to oxidized beer). As these become depleted the membranes of the yeast cells weaken, eventually leading to the death of the cells. You can regenerate these compounds at any time by taking the yeast through a well-oxygenated culture stage (i.e. a well oxygenated starter), allowing them to build these compounds back upto proper levels. If you do that (i.e. a proper starter every few batches) a yeast can be used near-indefinitely. . .with caveats.

The caveat is that every generation yeast accumulate a few mutations (the rate is approximately 1 mutation every 3 cell divisions, at least in the lab). Some of these mutations will alter the behaviour of the yeast - the beer environment & how we handle the yeast then acts as a form of selection, generally leading to a strain with undesired characteristics. Evolution - she is a *****!

Because of this, the conventional washing (home brewers) or yeast-cone transfers (breweries) allows yeasts to be used a handful of times. But, over time, the quality of the yeast degrade and they begin to accumulate undesired mutations, eventually requiring the yeast to be replaced

You can (at home, or in a brewery) propagate yeast indefinitely with a minimal accumulation of mutations, but it requires specialized skills and equipment. For many home brewers its not worth the effort, for many breweries its not worth the costs. The process is fairly simple - you have master stocks which you try and let divide as little as possible - usually by storing them frozen, in glycerol, at -80C. Small amounts of these stocks are taken, grown up to usable quantities, and then used like any other yeast in the brewery. Once reused for the desired number of times, another batch is restarted from the frozen stock. If needed, yeast managers will even plate out yeast to get single colonies (colonies arise from a single yeast cell, and are fairly genetically homogeneous). By selecting multiple single colonies & performing test ferments they can identify & re-isolate the starter stain.

I run a yeast bank that works (small-scale) like the process in the above paragraph. If you're interested I have a few blog posts & videos on it - just follow the link in my signature, and click on the "Yeast Wrangling" link.

Bryan
 
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